A Brompton folds a lot smaller than a Tikit. 15x24x35 in for the Tikit vs 10×22x22 in for the Brompton. (Both figures are off Wikipedia:
http://en.wikipedia.org/wiki/Tikit
http://en.wikipedia.org/wiki/Brompton_Bicycle
I have a Birdy and a Brompton and like the ride on both of them better than the Tikit I tried (I live in the NW so I kinda wish I liked the Tikit better - it's the home town player :-). The big win of the Brompton IMHO is two fold - the single big bag in the front is great around town as you end up with just one piece of luggage besides the bike and the small size fold really ends up mattering when you take the bike travelling.
But if you prefer the ride of a Tikit that is pretty important :-) Especially if you want to do longer rides on it.